This application is for the purchase of a laser scanning confocal microscope for the Department of Embryology, Carnegie Institution, Baltimore, MD. The confocal microscope is a new form of light optical microscope whose chief advantage is that it permits one to focus on a single plane in a thick object, without interference from out-of-focus parts of the specimen. Used in the epifluorescence mode, the confocal microscope allows one to resolve unprecedented detail in living cells, including single microtubules in the mitotic spindle, elements of the Golgi apparatus and endoplasmic reticulum, and individual bands on the polytene chromosomes of Drosophila. Our group proposes four uses for a confocal microscope. Gall will study the organization of giant chromosomes in the Amphibian oocyte nucleus, including the import and export of specific chromosomal proteins from the nucleus. Pagano will concentrate on the intracellular translocation and metabolism of lipids in living cells. Fire will study myogenesis in the free-living nematode Caenorhabditis using animals transformed with injected genes. Schwartz will examine individual DNA molecules immobilized in agarose gels. Each study involves fluorescent probes, but conventional fluorescence microscopy is difficult with the relatively thick specimens involved (whole cells, whole nuclei, whole animals). The confocal microscope is ideally suited for examining such thick specimens. Used in the epifluorescence mode, the confocal microscope will provide extraordinary spatial localization of molecular probes, permitting novel insight into biological processes.